Lysophosphatidic acid reverses Temsirolimus-induced changes in lipid droplets and mitochondrial networks in renal cancer cells.

Abstract

Increased cytoplasmic lipid droplets (LDs) and elevated AKT/mTOR signaling are characteristics of clear cell renal cell carcinoma (ccRCC). Lysophosphatidic acid (LPA), a potent lipid mitogen generated via autotaxin (elevated in ccRCC), can modulate tumor progression but its role in altering chemotherapeutic sensitivity to mTOR inhibitors is unclear and thus is the focus of the studies presented herein. Using malignant (A-498, 769-P and 786-O) and normal immortalized kidney (HK-2) cell lines, we investigated their cellular responsiveness to Temsirolimus (TEMS, mTOR inhibitor) in the absence or presence of LPA by monitoring alterations in AKT/mTOR pathway mediators (via western blotting), LDs (using LipidTOX and real-time PCR to assess transcript changes in modulators of LD biogenesis/turnover), mitochondrial networks (via immunofluorescence staining for TOM20 and TOM70), as well as cellular viability. We identified that TEMS reduced cellular viability in all renal cell lines, with increased sensitivity in the presence of an autophagy inhibitor. TEMS also altered activation of AKT/mTOR pathway mediators, abundance of LDs, and fragmentation of mitochondrial networks. We observed that these effects were antagonized by LPA. In HK-2 cells, LPA markedly increased LD size and abundance, coinciding with phospho-MAPK and phospho-S6 activation, increased diacylglycerol O-acetyltransferase 2 (DGAT2) mRNA (which produces triacylglycerides), and survival. Inhibiting MAPK partially antagonized LPA-induced LD changes. Collectively, we have identified that LPA can reverse the effects of TEMS by increasing LDs in a MAPK-dependent manner; these results suggest that LPA may contribute to the pathogenesis and chemotherapeutic resistance of ccRCC.